1. Field of Invention
The present invention relates to inverted-F antennas and more particularly to a dual-band inverted-F antenna with a branch line shorting strip mounted in a wireless communication device (e.g., cellular phone, PDA, etc.).
2. Description of Related Art
Wireless communication has known a rapid, spectacular development in recent years. Also, requirements for quality and performance of antenna mounted in a wireless communication device (e.g., cellular phone, PDA) are increased. In addition to the requirement of miniature antenna, multiple frequency band or ultra-wideband feature is also necessary for keeping up with the trend. Moreover, for aesthetic and practical purposes a miniature antenna is typically mounted within a wireless communication device (e.g., cellular phone). However, construction of the antenna can be very complicated for meeting the above requirements and needs. Thus, it is important to further improve the prior hidden antenna by fully taking advantage of the limited space in a wireless communication device (e.g., cellular phone or PDA).
Typically, a wireless communication device (e.g., cellular phone or PDA) is equipped with an inverted-F antenna therein. For example, U.S. Pat. No. 6,727,854 discloses a planar inverted-F antenna mounted in a cellular phone in FIG. 1. The antenna comprises a radiating device including left and right radiating elements (e.g., metallic strips) and an intermediate radiating elements (e.g., metallic patch) in which a feeding point 15 is formed at one end of the left radiating element, a shorting point 16 is formed at one end of the right radiating element opposing the feeding point 15, and three surface current pathways 10, 13, and 14 are formed in the intermediate, left, and right radiating elements respectively. Two different resonance frequencies are generated by these surface current pathways such that the antenna is able to operate in a GSM band or DCS band (i.e., dual-band capability).
However, the prior art suffered from several disadvantages. For example, only a single shorting line is provided. Further, its construction is relatively complicated. Furthermore, the surface current pathways are meandered, resulting in a narrowing of bandwidth (i.e., only suitable for dual-band applications). Moreover, its adjustment is difficult in practice. Thus, the need for improvement still exists in order to overcome the inadequacies of the prior art.